Depression Is Killing. Don't Know How I Got This Problem,

Depression is killing. Don't know how I got this problem, unknowingly my mind keeps on thinking and due to which my body is not gaining fat. I joined gym but to no use, eat lots of food but never got body mass but my tension making me very thin. I was weighing 96 kilos in 2010 now just 73. My legs are very thin, even after lots of exercise never gained mass in my legs due to which I am looking very thin.